1. Field of the Invention
The present invention relates to a liquid crystal display panel and a manufacturing method thereof, and is characterized in that in dripping liquid crystal to one of a pair of substrates and sealing one substrate to another substrate using a sealing material, the interference between the dripped liquid crystal and the sealing material and the sealing failure attributed to the intrusion of the liquid crystal or air into the sealing material at the time of sealing can be prevented.
A liquid crystal display device has been popularly used in various monitors, a display device of electronic equipment or a television receiver set. The liquid crystal display device is basically constituted by assembling a liquid crystal display panel which seals liquid crystal between a pair of substrates, a drive circuit which drives the liquid crystal display panel and the like.
FIG. 8 is a cross-sectional view for schematically explaining a constitutional example of the liquid crystal display panel. Here, the explanation is made by taking an active-matrix-type liquid crystal display panel which uses a thin film transistor (TFT) as an active element which selects each pixel on one of a pair of (hereinafter, also referred to as two) substrates as an example. However, the present invention is not limited to the active-matrix-type liquid crystal display panel and is also applicable to a liquid crystal display panel of other type in the same manner.
In FIG. 8, the liquid crystal display panel 9 is configured such that liquid crystal 5 is sandwiched between a substrate (TFT substrate) 1a on which pixels are formed using a thin film transistor and a color filter substrate (CF substrate) 1b which forms three colors of red (R), blue (B), green (G), and peripheries of both substrates are sealed by a sealing material 7. As a manufacturing method of such a liquid crystal display panel 9, two methods, that is, a vacuum filling method and a dripping method have been roughly proposed. Here, in FIG. 8, spacers 4 are formed as so-called columnar spacers (SOC) which are directly and fixedly formed on the CF substrate 1b side. However, the method which scatters bead-like spacers on one substrate is also known. In the dripping-type liquid crystal display panel, the columnar spacers are used in many cases and hence, in the manufacturing method of the present invention which is explained hereinafter, the liquid crystal display panel which uses the columnar spacers is explained.
The vacuum filling method is a method which assembles a TFT substrate 1a and a CF substrate 1b and, thereafter, fills liquid crystal 5 in a space which is formed by a gap defined between the TFT substrate 1a and the CF substrate 1b by way of spacers 4. On the other hand, the dripping method is a method which, first of all, drips a predetermined quantity of liquid crystal 5 to either one of a TFT substrate 1a or a CF substrate 1b and, thereafter, another substrate is overlapped to one substrate thus performing the assembling of a liquid crystal display panel 9 and the filling of the liquid crystal 5 simultaneously. Usually, a gap between the TFT substrate 1a and the CF substrate 1b of the liquid crystal display panel 9, that is, a cell gap is 3 μm to 5 μm and hence, the cell gap is extremely small.
To completely fill the liquid crystal in the space defined by the gap of 3 μm to 5 μm using the vacuum filling method, first of all, the TFT substrate 1a and the CF substrate 1b are adhered to each other and peripheries of both substrates are adhered to each other using the sealing material 7. Here, a liquid crystal filling port is formed in a portion of the sealing material 7. Next, a vacuum evacuation operation of a space defined by the adhesion of the TFT substrate 1a and the CF substrate 1b is performed using a vacuum chamber or the like. Thereafter, liquid crystal is brought into contact with the liquid crystal filling port and the liquid crystal is filled into the inside of the adhesion gap (space) between the TFT substrate 1a and the CF substrate 1b by making use of a capillary phenomenon and the pressure difference between pressures inside and outside the space.
However, when this method is adopted, the vacuum evacuation of the cell gap space of 3 μm to 5 μm and the injection operation of the liquid crystal in the cell gap space require an extremely long time. Particularly, along with increase of a demand for a narrower gap of the liquid crystal display panel hereinafter, it is predicted that a filling time of liquid crystal is steadily increased. Further, it is necessary to provide a step which closes a filling port after the completion of filling of the liquid crystal and hence, the liquid crystal filling step is one of factors which elevate a manufacturing cost.
On the other hand, when the dripping method is adopted, this method is a method which performs panel assembling for adhering the TFT substrate 1a and the CF substrate 1b and filling of the liquid crystal simultaneously and hence, a vacuum evacuation operation which brings the space having the adhesion gap of 3 μm to 5 μm defined between the TFT substrate 1a and the CF substrate 1b into a reduced-pressure atmosphere is unnecessary. Further, an operation to seal the liquid crystal filling port is no more necessary. Further, since the liquid crystal is dripped using a dispenser or the like, liquid crystal filling time is also accelerated. Accordingly, by adopting the dripping method, it is possible to largely shorten the time necessary for filling the liquid crystal in the inside of the adhesion gap between the TFT substrate 1a and the CF substrate 1b compared to the vacuum filling method.
FIG. 9A to FIG. 9E are explanatory views of a manufacturing method of a liquid crystal display panel using a dripping method. Here, the explanation is made with respect to an example in which columnar spacers 4 explained in conjunction with FIG. 8 are preliminarily incorporated in the CF substrate 1b. 
First of all, a sealing material 7 is applied to a TFT substrate 1a in a frame shape using a dispenser 70 in a state that the sealing material 7 surrounds a display region 2 (FIG. 9A). A predetermined quantity of liquid crystal 5 is dripped at positions inside the sealing material 7 using a dispenser 50 (FIG. 9B). Two substrates (the TFT substrate 1a and the CF substrate 1b) are aligned and adhered to each other in a reduced-pressure atmosphere (FIG. 9C).
After completion of the adhesion, two substrates are taken out from the reduced-pressure atmosphere and are brought into an atmospheric pressure atmosphere. For curing the sealing material 7, treatment such as the radiation of ultraviolet lays using an ultraviolet lamp 18 in conformity with a curing condition of the sealing material 7 or heating of the adhered substrates are performed (FIG. 9D). Finally, two substrates are cut into individual panels having a predetermined panel size (FIG. 9E). The liquid crystal display panel 9 is completed by performing the above-mentioned steps.
There are many patent documents which disclose the related art on the filling of liquid crystal by a dripping method. For example, Japanese Patent No. 3210109 (patent document 1) discloses a technique which prevents dripped liquid crystal from flowing to a neighboring portion by forming a bank (weir) on a sealing portion. Further, Japanese Patent No. 3281362 (patent document 2) discloses the constitution in which concave-convex structure is provided to respective seal portions of two substrates, these concave-convex structures are fitted to each other, and a sealing material is applied to outer peripheries of the concave-convex structures thus preventing a contact between liquid crystal and the sealing material.
2. Description of the Related Arts
The filling of liquid crystal by the dripping method shown in the related art mainly uses a liquid crystal filling technique of a large-sized liquid crystal display device having a large display screen size. However, such a liquid crystal filling technique is not applied to an intermediate-size or miniaturized liquid crystal display device having a small display screen sizes.
This is because that the application of the liquid crystal filling technique of the large-sized liquid crystal display device has a following drawback. That is, as shown in FIG. 9B, with respect to the large-sized liquid crystal display device having the large display screen, a dripping quantity, dripping positions and the like can be adjusted by dripping the liquid crystal at a large number of dripping points from the dispenser 50, while with respect to the intermediate-size or the miniaturized liquid crystal display device having the small display screen, the number of dripping points from which the liquid crystal is dripped to a display screen (also referred to as a display region) is remarkably small compared to the number of dripping points for the large-sized liquid crystal display device and hence, the adjustment of the dripping quantity and the dripping positions are extremely difficult.
Accordingly, the size of the liquid crystal display panel is miniaturized, a distance between the dripped liquid crystal and the sealing material is small and hence, the sealing material is brought into contact with the liquid crystal before being cured in the sealing step thus generating a leak path in the sealing material or generating the intrusion of air or liquid crystal into the sealing material whereby the sealing material is deteriorated. Further, a sealing effective width is decreased thus lowering the reliability of the sealing material.
FIG. 10A and FIG. 10B are schematic views for explaining the sealing failure which occurs when the sealing material is brought into contact with the liquid crystal before being cured. FIG. 10A is the explanatory view of the leak path in the sealing material, wherein numeral 7 indicates a sealing material, numeral 4 indicates a liquid crystal side (display region side), and numeral 6 indicates an atmosphere side or a reduced-pressure atmosphere side. When liquid crystal 5 in the display region 4 is brought into contact with the sealing material 7 before being cured, the liquid crystal 5 breaks the soft sealing material 7 thus forming leak paths B through which the liquid crystal 5 flows out to the atmosphere side or the reduced-pressure atmosphere side.
Further, FIG. 10B is a view for explaining the occurrence of intrusion of air or liquid crystal into the sealing material. When the liquid crystal 5 reaches the sealing material 7 before being cured, the liquid crystal intrudes into the sealing material 7 thus narrowing an effective width of the sealing material 7. Further, this intrusion also occurs on the atmosphere side or the reduced-pressure atmosphere side. As a result, the effective sealing width W is narrowed from both sides and hence, the sealing material 7 cannot acquire a sufficient sealing effect.
It is an object of the present invention to provide a liquid crystal display panel and a manufacturing method thereof which can prevent the occurrence of a leak path of a sealing material and the reduction of an effective sealing width which are brought about due to a contact of liquid crystal with an uncured sealing material in a sealing step.